A method this type is known from EP 0.335.313-A-2. For etching silicon dioxide on the surface of semiconductor substrates, such a substrate is placed in a plastic-lined stainless steel etching chamber and then treated, if appropriate under reduced pressure, with a corrosive mixture of acetic acid, water or methanol (preferably 100%) and hydrogen fluoride. The chamber is first filled with the requisite amount of acetic acid, the requisite amount of hydrogen fluoride then being introduced. The various sources or feeds of hydrogen fluoride and acetic acid are each closable by means of valves. The piping system is made either of stainless steel or of plastic, such as perfluoroalkoxy (PFA).
Although a method of this type yields excellent etching results, there is the problem that, when the hydrogen fluoride shut-off valve is opened, on the one hand hydrogen fluoride flows into the etching chamber, but some acetic acid inevitably diffuses back via said shut-off valve into the piping system for HF. Such an amount is found to be very small in practice and not to have an adverse effect on the rate of etching, but it has been found that the upstream stainless steel piping system as a result is attacked as far as the BF source and that this can result in undesirable metal contaminants on the semiconductor substrate in subsequent etching operations.
This means that it is sometimes necessary to replace such a piping system and that in any event it is necessary to subject such a piping system to a regular check.
Both operations impede the process operation and are disadvantageous.
In EP 0.335.313-A-2 mentioned above, a method and device are described, wherein two etch gases from a ft and a second source are being supplied through a common conduit to an auxiliary chamber. In this auxiliary chamber a plasma is generated and this is transferred to the reactor. The etching gases used are CF4 and O2. It is of importance that both gases are being supplied simultaneously and preferably continuously from the source through the auxiliary chamber to the process chamber.
Such a method does not give a solution for the problem mentioned above i.e. the aggressively of a mixture of HF and another etchant and/or catalyst such as acetic acid, formic acid or water.